Industries, including security and defense, require instruments to detect and identify a variety of compounds, including toxic industrial chemicals and materials, explosives, chemical warfare agents (CWA), biological agents and other potentially dangerous agents. Due to the current heightened fears of terrorist activity, highly sensitive, selective, and accurate detecting instruments are particularly desired for security screening purposes, such as in airports.
The instruments currently employed for detection of explosives and CWAs include ion mobility spectrometers, mass spectrometers, liquid chromatographs, and gas chromatographs. These instruments, however, have low sensitivity and low selectivity; consequently, they suffer from high false alarm rates. A measure of the sensitivity of a detector is its limit of detection. In the case of the currently employed technologies, the limit of detection can be significant, thereby allowing trace chemicals to go undetected.
In addition to having low sensitivity, the current instruments also suffer from high false alarm rates. False positive alarms can be time-consuming and cause delays in the screening process. More importantly, high false alarm rates reduce the confidence of the user in the instrument producing the false alarms, which discourages the user from using the instrument. Obviously, security suffers when the detecting instrument is not utilized.
Recently, Surface Enhanced Raman Spectroscopy (SERS) has been developed for the detection of molecules with extreme sensitivity. In principle, the limit of detection for SERS is as low as a single molecule, though this is not realized in field conditions. SERS also has a very high molecular discrimination capability due to the intrinsic nature of the Raman scattering. SERS requires the deposition of particles to be identified onto a textured metal surface or substrate. The presence of a large variety of compounds can create problems from high field contamination because the Raman spectroscopic signatures become unclear or unidentifiable.
The present invention addresses the problem of detecting and identifying compounds. The present invention advances the art with a SERS ion detector with an ion separation pre-filter.